1. Field of the Invention
The present invention generally relates to a display device, and more particularly, to a reflective type display device of which a screen may be watched through lighting provided from an external environment.
2. Description of the Related Art
Reflective type display devices, commonly referred to as “electronic paper”, are variously developed as a screen display element together with a Liquid Crystal Display (LCD), a plasma display panel, and an electro luminescence element. The reflective type display device includes a thin flexible film coated with pigment particles so as to display characters or images when the pigments are driven by an electric signal and easily secure flexibility while implementing a clear image quality as if an image is printed on an ordinary paper. A drive layer of the reflective type display device is made of pigment particles that contain pigments of at least two different colors in which transparent electrodes are arranged on the top surface and the bottom surface of the drive layer, respectively, so as to drive the pigment particles. In a reflective type display device that implements only a black and white screen, black and white pigments are introduced into the pigment particles, respectively.
In general, the reflective type display device allows the screen to be watched through lighting provided from an external environment. However, as the reflective type display device is mounted on a device that is used in an everyday environment like an electronic book terminal, the necessity of a separate lighting device has increased. In fact, a lighting device such as a compact light emitting diode equipped on an electronic book terminal has now appeared on an after-market. Typically, the drive layer made of pigment particles does not transmit light. Thus, when the display device is provided with a lighting device, the lighting device is arranged on the top surface of the drive layer.
FIG. 1 illustrates a structure in which a lighting device is provided in a conventional reflective type display device 10.
As described above, the display device 10 includes a drive layer 11 which is made of pigment particles 11a in which transparent electrodes 13b and 13a are disposed on the top surface and the bottom surface of the drive layer 11, respectively. At least one of the transparent electrodes 13a and 13b is an active element. For example, the transparent electrode provided on the bottom surface of the drive layer 11 may be made of a thin film transistor. The other of the transparent electrode may be configured as a passive element. For example, the transparent electrode provided on the top surface of the drive layer 11 may be made of an Indium Tin Oxide (ITO) film. The pigment particles 11a are driven in response to a signal applied to the transparent electrodes 13a and 13b such that black or white pigment 11b is oriented toward the top surface of the drive layer 11. Thus, the display device 10 outputs a screen.
As described above, the lighting device is disposed on the display device 10, specifically, on the top surface of the drive layer 11. The lighting device is provided with a light source 15a such as a light emitting diode and a light guide plate 15b. The light guide plate 15b may be attached to the transparent electrode 13b positioned on the top surface of the drive layer 11. In addition, the display device 10 is provided with a protection film 17 attached to the light guide plate 15b so as to prevent damage of the light guide plate 15b. This is because, when damage such as a scratch occurs on the light guide plate 15b which substantially forms a screen transmission region, image quality may be degraded. Light emitted from the light source 15a is diffused to a screen display region of the display device 10 through the light guide plate 15b and absorbed to or reflected by the pigment particles 11a of the drive layer 11, thereby allowing a screen implemented on the display device 10 to be watched even in a dark environment.
However, the lighting device has a disadvantage in that it is difficult for the lighting device to provide lighting evenly to the screen display region. In other words, at a point distant from a light source, the lighting at the point is lowered. Accordingly, when the lighting device is installed in the reflective type display device, there is a limit in fabricating the screen display region in a large size. In order to provide lighting evenly over the entire screen display region, a plurality of light sources may be arranged at regular intervals. However, this also causes an increase of manufacturing costs. Further, a reflection pattern may be formed on the light guide plate so as to provide lighting evenly over the screen display region. However, since the output screen passes through the light guide plate, the reflection pattern becomes the cause of degradation of image quality.